We propose to examine gene expression in regions of embryonic ectoderm during the establishment of lens and non-lens lineages. For the past several years my laboratory has been studying the development of the lens because the ontogeny of embryonic ectoderm can be so effectively manipulated to analyze the inductive tissue interactions leading to determination of the lens lineage and because the development of this tissue is so well suited to an analysis of gene expression. Our findings and review of the literature have led us to question some existing dogma and to formulate our own model for how inductive interactions cause lens formation. We also believe that cell determination may involve at least two majors steps in this tissue: acquisition of a strong lens-forming bias early in development followed by an irreversible commitment step somewhat later. Our first goal in the proposed work is to use crystallin gene probes as markers for testing some elements of our lens induction model. However, to examine the early stages of this process we propose to identify mRNAs that are expressed earlier than the crystallins, in particular regions of ectoderm that have a lens-forming bias or have lost the ability to form a lens. We have identified one such gene and have isolated two others which in preliminary analyses appear to have these properties. We plan to map the temporal and spatial patterns of expression of genes that are expressed in a region-specific manner in the ectoderm to see if expression correlates with known developmental properties of these tissues in vivo. These genes will also be used as markers in transplantation and explant experiments designed to clarify the important inductive interactions leading to lens formation. Finally, we propose to develop functional assays to test whether genes that are expressed in either the early lens or non-lens ectodermal lineages are important in establishing the biological properties of these lineages.